To provide a distortion measuring apparatus, which enables highly accurate measurement of distortions, even under the environment of relatively large temperature fluctuations.

This apparatus has a strain gauge, in which first and second resistors 2 and 3 are arranged in proximity to each other with the code of a gauge ratio opposite to each other with respect to as a prescribed distortion, a first bridge circuit corresponding to the first resistor 2, a second bridge circuit corresponding to the second resistor 3 and a differential amplification means 14 (third amplifier) for amplifying the difference between a signal, based on the output of the first bridge circuit and a signal which is based on the output of the second bridge circuit.